1. Field of the Invention
The present invention relates to an engine control apparatus for a hybrid vehicle with an engine and a motor for driving the vehicle mounted thereon. More specifically the present invention pertains to an engine control apparatus under a fuel cut control that is carried out at the time of speed reduction, for example, through a braking operation.
2. Description of the Related Art
In an engine mounted on a vehicle, a fuel cut control that temporarily cuts a supply of fuel injected into the engine is generally carried out at the time of speed reduction, for example, through a braking operation, in order to improve the fuel consumption rate as well as emission of the gaseous exhausts. The fuel cut control under the speed reduction causes an abrupt decrease in output of the engine, which results in an abrupt increase in frictions including a pumping loss. The increased frictions enhance engine brake and may damage a good ride.
A technique disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 59-100941 has been proposed to above such problems. The prior art technique utilizes an atmospheric air introduction passage, which bypasses a throttle valve and is arranged in an intake air conduit, and a control valve arranged in the atmospheric air introduction passage, and opens the control valve under the fuel cut control. Connection of a cylinder with the atmospheric air introduction passage by opening the control valve under the fuel cut control enables a piston to go up and down in the total volume of the cylinder, thereby reducing the pumping loss.
The prior art technique has the effect of reducing the pumping loss while an intake valve and an exhaust valve are open. In case that both the intake valve and the exhaust valve are closed, however, the air is compressed and expanded in only the volume of the cylinder. This causes a large pumping loss, which enhances engine brake and may damage a good ride. While the intake valve and the exhaust valve are closed, the compression and expansion of the air in the cylinder increases the temperature of the gas in the cylinder, thereby causing a cooling loss.
A hybrid vehicle, on which an engine and a motor work in combination, has been proposed and expected to improve the fuel consumption rate and the emission characteristics of the gaseous exhausts. It is required to solve the above problems under the fuel cut control in such a hybrid vehicle.